This invention relates to lead terminal arrangements for electronic circuit components such as semiconductor devices and to methods of mounting such components.
The arrangement of a lead terminal 3 of a conventional electronic circuit component 1 such as a semiconductor device is described herein with reference to FIG. 4. The component 1 has a package body 2 encapsulating a semiconductor element or the like and lead terminals 3 extending out of the package body. Each of the lead terminals 3 has an inserted tip portion 3a, a cut dumb bar portion 3b and a butt portion 3c. The tip portion 3a is inserted into a lead terminal hole 11 in a printed circuit board 10 when the component 1 is to be mounted thereon. The tip portion 3a has a width which is selected to be smaller than the diameter of the hole 11. The cut dumb bar portion 3b is formed as a result of punching out a dumb bar coupling between the terminals 3 which is provided to hold the terminals together before the package body 2 is molded. The width of the cut dumb bar portion 3b is designed to be larger than the diameter of the lead terminal hole 11 so as to provide a gap between the bottom of the package body 2 and the top of the circuit board 10 when the component 1 is mounted thereon. The width of the butt portion 3c is designed to be larger than that of the inserted tip portion 3a so that the terminal 3 has enough strength at the butt portion. After the component 1 is mounted on the printed circuit board 10, the lead terminals 3 are connected to the bottom of the board by solder 12 using a flow-soldering process or the like. During that process, a soldering flux vaporizes so that the gas therefrom is released to the outside through the lead terminal holes 11 and through the gap between the top of the circuit board 10 and the bottom of the package body 2. Thus, the gap is provided to permit release of the vaporized flux from the top of the circuit board 10 to the outside.
The conventional electronic circuit component 1 has the problem described hereinafter. Since the lead terminal 3 is connected at its tip portion 3a only to the bottom of the printed circuit board 10 by the solder 12, the component is likely to vibrate when the board is vibrated. Because of the vibration of the component, the lead terminal 3 undergoes stress which is likely to concentrate at the boundary A between the tip portion 3a and the cut dumb bar portion 3b of the terminal, at which the width of the terminal changes sharply. For that reason, the lead terminal 3 is likely to undergo metal fatigue at the boundary A so as to be bent or broken.